The exhaust gas emitted from an internal combustion engine is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOx”) as well as condensed phase particulate materials (liquids and solids) including carbon that constitute particulate matter (“PM”). Catalyst compositions typically disposed on catalyst supports or substrates are provided in an engine exhaust system to convert certain, or all of these exhaust constituents into non-regulated exhaust gas components.
One type of exhaust treatment technology for reducing CO and HC emissions is an oxidation catalyst device (“OC”). The OC device includes a flow-through substrate and a catalyst compound applied to the substrate. One type of exhaust treatment technology for reducing NOx emissions is a selective catalytic reduction (“SCR”) device that may be positioned downstream of the OC device. An exhaust treatment technology in use for high levels of PM reduction may include a particulate filter (“PF”) device that traps PM, which may be positioned downstream of the OC device and the SCR device. Regeneration is the process of removing the accumulated PM from the PF device.
A PM oxidation rate represents an amount of PM that is oxidized within the PF device per a unit of time during regeneration. Sometimes the PM is loaded or trapped within the PF device such that the PM is relatively more resistant to oxidation. For example, if the PM is densely packed in the PF device, or has a relatively high concentration of hydrocarbon, this may make the make the PM relatively more resistant to oxidation. As a result, higher input exhaust temperatures and longer heating times may be needed during regeneration, which in turn affects fuel consumption. Accordingly, it is desirable to provide a regeneration strategy that is more efficient when compared to some exhaust gas treatment systems currently available.